Apparatus and method of using flexible printed circuit board in optical transceiver device

ABSTRACT

This invention relates to a flexible printed circuit board that is used in connection with an optical transmitter, receiver or transceiver module. In one embodiment, the flexible printed circuit board has flexible metal layers in between flexible insulating layers, and the circuit board comprises: (1) a main body region orientated in a first direction having at least one electrical or optoelectronic device; (2) a plurality of electrical contact pads integrated into the main body region, where the electrical contact pads function to connect the flexible printed circuit board to an external environment; (3) a buckle region extending from one end of the main body region; and (4) a head region extending from one end of the buckle region, and where the head region is orientated so that it is at an angle relative to the direction of the main body region. The electrical contact pads may be ball grid arrays, solder balls or land-grid arrays, and they function to connect the circuit board to an external environment. A driver or amplifier chip may be adapted to the head region of the flexible printed circuit board. In another embodiment, a heat spreader passes along a surface of the head region of the flexible printed circuit board, and a window is formed in the head region of the flexible printed circuit board. Optoelectronic devices are adapted to the head spreader in such a manner that they are accessible through the window in the flexible printed circuit board.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to the following co-pending applications,each assigned to the Assignee of the present invention.

application Ser. No. 09/749,279, filed Dec. 26, 2000, entitled“Apparatus For Holding An Optical Element”;

application Ser. No. 09/749,282, filed Dec. 26, 2000, entitled“Attenuator and Conditioner”;

application Ser. No. 09/749,283, filed Dec. 26, 2000, entitled“Optoelectronic Mounting Structure”;

application Ser. No. 09/749,284 filed Dec. 26, 2000, entitled “OpticalTransmitter, Receiver or Transceiver Module”;

application Ser. No. 09/749,285, filed Dec. 26, 2000, entitled “HousingAnd Mounting Structure”;

application Ser. No. 09/749,286, filed Dec. 26, 2000, entitled “OpticalPower Control System”; and

application Ser. No. 09/749,287, filed Dec. 26, 2000, entitled “Processfor Coupling Optical Elements to Optoelectronic Devices”.

FIELD OF THE INVENTION

This invention relates to a flexible printed circuit board that is usedin connection with an optical transmitter, receiver or transceivermodule.

BACKGROUND OF THE INVENTION

Fiber optics are one of the most important new media for transmittinginformation. Fiber optics are capable of carrying enormous quantities ofvoice, data and video traffic on light impulses over hair-thin glassfibers. Fiber optics transmit more information and data over a shorterperiod of time than circuit-transmission media. For example, opticalsignals may be transmitted over fiber optics with losses of less than0.1 dB/km. In sharp contrast, data generally is transmitted over a pairof twisted copper wires with losses of up to 50 dB/km. The capabilitiesof fiber optics have fundamentally changed communications.

The fiber optics industry has exploded as the Internet andtelecommunication field have created a skyrocketing demand forbroadband, high-speed pipe lines to carry data. Long-span fiber opticnetworks of 100 kilometers or more carry bandwidth ranging from 40 to 50giga bites per second. Similarly, high-speed fiber optics are capable ofconnecting wide-area networks of approximately 200 kilometers. Also,fiber optics may connect metropolitan networks of 500 meters to 2kilometers, such as connecting one building to another building. Thelargest growth area for high-speed fiber optics, however, is connectingdistances of less than 300 meters. In this sub-300 meter orshort-distance market, fiber optics are used for a wide variety ofpurposes, including connecting computers within a room and linkingrouters, switches and transport equipment.

While significant progress has been made in the area of fiber optics,more wide-spread use is dependent upon the availability of a low cost,easy-to-use and efficient (i.e., low loss of light) optical transmitterand receiver module to link fiber optics to various electronic devicesand components such as computers and routers. A critical aspect of sucha module is the accurate alignment and attachment of the individualoptical fibers to the electronic devices that transmit and receive lightstreams to and from the optical fibers. These electronic devices, knownas optoelectronic devices, use optical and electronic technology oroptoelectronics to convert electrical signals into optical radiation orlight and transmit the radiation into optical fibers. Otheroptoelectronic devices receive optical radiation from optical fibers andconvert it into electrical signals for processing. Accurate alignmentand attachment of the individual optical fibers to the optoelectronicdevices is essential to achieving a good and efficient opticalconnection, one that produces a low loss of light at the interfacebetween the optical fibers and the optoelectronic devices.

A known method for precisely coupling optical fibers to optoelectronicdevices is active alignment. Specifically, a photo-detector is placed atone end of an optical fiber, and an optoelectronic device, such as avertical cavity surface emitting laser, is placed near the other end ofthe optical fiber. After turning on the laser, the optical fiber ismanipulated manually around the light-emitting surface of the laseruntil the photo-detector detects the maximum amount of optical radiationas indicated by an output electrical signal. Similarly, a photo-detectorcan be actively coupled to an optical fiber by transmitting laser lightinto one end of an optical fiber and manually adjusting the position ofthe other end of the optical fiber relative to the photo-detector untilthe detector receives the maximum amount of optical radiation.

Actively aligning an array of optical fibers to an array ofoptoelectronic devices is not practical because the dimensions of anoptoelectronic device and the cross-section of an optical fiber aresmall and multiple dimensions of rotation and translation motion must becontrolled. The active alignment process to connect even a singleoptical fiber strand to an optoelectronic device is usuallytime-consuming and requires knowledge, skill and expertise. The activealignment process is particularly laborious and time-intensive when anumber of optical fibers must be individually aligned to an array ofoptoelectronic devices. This process requires a variety of relativelycomplex and costly components that significantly increase thefabrication costs to produce precisely aligned optical devices.Moreover, during the active alignment process, optoelectronic devicesemit a significant amount of optical power and energy. The heatgenerated by the devices can produce thermal strain that may cause theoptical fibers and the optoelectronic devices to be misaligned.

Various passive alignment techniques have been developed, such as theuse of guide pins and holes, to attempt to provide fast, easy andsimultaneous alignment and attachment of an array of optical fibers tooptoelectronic devices. Passive alignment typically indicates atechnique for aligning a laser and an optical fiber that does notrequire the laser to be turned on during the alignment process; whereasan “active” technique requires the laser to be turned on. However, thesepassive alignment techniques often do not provide a precision couplingof the optical fibers to optoelectronic devices.

Accordingly, there is a need in the art to provide a method andapparatus for precise, fast and easy alignment and attachment of opticalfibers to optoelectronic devices, which may be mounted on a circuitboard. In addition, there is a need in the art to provide an inexpensivemethod and apparatus for aligning and attaching optical fibers tooptoelectronic devices so that the method and apparatus are suitable formass production. Finally, there is a need in the art for a smallapparatus coupling optical fibers to optoelectronic devices so that theapparatus can easily be mounted on a circuit board.

SUMMARY OF THE INVENTION

In view of the above-stated disadvantages of the prior art, an object ofthe present invention is to provide a flexible printed circuit boardthat may be used in connection with an optical transmitter, receiver ortransceiver module.

Another object of the present invention is to provide an apparatus andprocess for quickly, easily and precisely aligning and connecting atleast one optical fiber to at least one optoelectronic device by usinghighly precise machinery and adhesive.

Another object of the present invention is to provide an apparatus andprocess for aligning and connecting at least one optical fiber to atleast one optoelectronic device while maintaining a gap between at leastone optical fiber and at least one optoelectronic device.

Another object of the present invention is to provide an apparatus andprocess for quickly, easily and precisely aligning and connecting atleast one optical fiber to a wide variety of device(s) or object(s) byusing highly precise machinery and adhesive.

Another object of the present invention is to provide an inexpensivemethod and apparatus for aligning and connecting at least one opticalfiber to at least one optoelectronic device so that the method andapparatus are suitable for mass production.

Another object of the present invention is to provide an inexpensivemethod and apparatus for aligning and connecting at least one opticalfiber to a wide variety of device(s) or object(s) so that the method andapparatus are suitable for mass production.

Another object of the present invention is to provide a small apparatusfor coupling at least one optical fiber to at least one optoelectronicdevice so that the apparatus can easily be mounted on a circuit board.

In accordance with the first object of the present invention, anembodiment of the flexible printed circuit board comprises: (1) a mainbody region orientated in a first direction having at least oneelectrical or optoelectronic device; (2) a plurality of electricalcontact pads integrated into the main body region, where the electricalcontact pads function to connect the flexible printed circuit board toan external environment; (3) a buckle region extending from one end ofthe main body region; and (4) a head region extending from one end ofthe buckle region, and where the head region is orientated so that it isat an angle relative to the direction of the main body region. Theelectrical contact pads may be ball grid arrays, solder balls orland-grid arrays, and they function to connect the circuit board to anexternal environment. A driver or amplifier chip may be adapted to thehead region of the flexible printed circuit board. In anotherembodiment, a heat spreader passes along a surface of the head region ofthe flexible printed circuit board, and a window is formed in the headregion of the flexible printed circuit board. Optoelectronic devices areadapted to the head spreader in such a manner that they are accessiblethrough the window in the flexible printed circuit board.

In accordance with other aspects of the present invention, an opticaltransmitter, receiver or transceiver module is provided that includes aflexible printed circuit board that is bent at an angle, forming a headregion, buckle region and main body region. The flexible printed circuitboard supports the electrical components and circuitry of the presentinvention.

An array of optoelectronic devices, a driver or amplifier chip, aphoto-detector, conducting lines, and electronic components may bemounted on a first surface of the head region of the flexible printedcircuit board. The optoelectronic devices send and or receive light toand from optical fibers. The optoelectronic devices may be mounted ontop of a spacer that may be attached to the head region of the flexibleprinted circuit board. The spacer raises the height of theoptoelectronic devices so that they may efficiently communicate with theoptical fibers and other electrical components that are mounted on thehead region of the flexible printed circuit board. Alternatively, theoptoelectronic devices may be mounted on an optoelectronic mountingstructure that is accessible through a window in the flexible printedcircuit board. When the optoelectronic devices function as emitters foremitting optical signals into optical fibers, they may be oxide-confinedvertical cavity surface emitting lasers; if the optoelectronic devicesfunction as receivers for receiving optical signals from optical fibers,they may be photo-detectors formed on a semiconductor chip. The driveror amplifier chip modulates and drives the optoelectronic devices. Anoptical power control system may monitor, regulate and stabilize thetemperature, power and wavelength of the optoelectronic devices.Additionally, an attenuator may improve the performance of theoptoelectronic devices by attenuating the optical energy emitted fromthe devices. Similarly, a conditioner may improve the performance of theoptical fibers by conditioning the launch of the optical energy into thefibers.

The remaining electrical components and circuitry of the optical modulemay be located on the main body region of the flexible printed circuitboard.

The buckle region of the flexible printed circuit board, the regionconnecting the main body region and head region, absorbs any stress thatmay occur in connecting a fiber optic cable to the present invention andassists in providing alignment between the optical fibers andoptoelectronic devices.

A first ferrule, packaging an array of optical fibers, is mounted on topof the array of optoelectronic devices on the first surface of the headregion of the flexible printed circuit board. Highly precise machineryoptically aligns aligns the array of optical fiber in the first ferruleto the array of optoelectronic devices. A gap or interstitial space isestablished between a second end of the first ferrule and a top surfaceof the optoelectronic devices. Optical adhesive is dispensed in thespace or gap between the first ferrule and the optoelectronic devices soas to maintain the precise axial alignment of the array of opticalfibers to the array of optoelectronic devices. The optical adhesiveprovides a optically transparent and stable medium between theoptoelectronic devices and the fibers.

After the optical adhesive is cured, a dam may be formed on the firstsurface of the head region of the flexible printed circuit board. Asecond adhesive is dispensed inside the dam, and the second adhesivefurther mechanically stabilizes the first ferrule to the flexibleprinted circuit board. The second adhesive also protects the circuitryin the immediate vicinity of the optical fibers and optoelectronicdevices. For airtight sealing of the optical module, the surface area ofthe second adhesive may be covered with a third layer, such as a gelsilicon resin.

After the first ferrule is firmly attached to the head region of theflexible printed circuit board, the circuit board is wrapped around andattached to a circuit board mounting structure with an adhesive.

A housing snaps or otherwise mounts with screws, adhesives or othermeans onto a first end of the circuit board mounting structure,enclosing the head region of the flexible printed circuit board alongwith the first ferrule that is mounted on the head region. The firstferrule fits inside a longitudinal cavity extending from a first end ofthe housing to a second end of the hous ing. Ridges inside thelongitudinal cavity grab and hold the first ferrule in place.

In operation, a fiber optic cable from an external system is brought inproximity to the housing to create an optical connection. A secondferrule is located at one end of the fiber optic cable, and the secondferrule is designed to mate with the second end of the housing. Thesecond ferrule is inserted into the second end of the housing and ridgesin the housing's longitudinal cavity engage and hold the second ferrulein place. Once inside the longitudinal cavity, the second ferrule mateswith the first ferrule by engaging guide pins located on a front end ofthe first ferrule with guide holes located on a front end of the secondferrule. As a result, the array of optical fibers packaged in the twoferrules are axially aligned. Upon mating the ferrules together, lightmay be transmitted from the fiber optic cable through the two ferrulesand to the optoelectronic devices that are adapted to the flexibleprinted circuit board.

A further significant aspect of the present invention involves a processby which the first ferrule is aligned and connected to the array ofoptoelectronic devices, according to a preferred embodiment of theinvention. A process of aligning and connecting the first ferrule to thearray of optoelectronic device comprises the following steps:

-   -   1. Aligning the optical fiber(s) packaged in the first ferrule        with the optoelectronic device(s) so that each optical fiber is        optically aligned to a corresponding optoelectronic device(s);    -   2. Depositing optical adhesive on a top surface of the        optoelectronic device(s);    -   3. Placing the first ferrule on top of the optical adhesive        while maintaining the alignment of step 1;    -   4. Tacking and curing the optical adhesive; and    -   5. Forming a dam around the first ferrule that is mounted on the        head region of the flexible printed circuit board, dispensing        adhesive and curing the adhesive.

Although the above-stated process has been discussed in terms ofaccurately aligning and attaching the first ferrule to the array ofoptoelectronic devices, the same process may be used to accurately alignand attach a single optical fiber or an array of optical fibers to asingle optoelectronic devices or an array of optoelectronic devices.Similarly, the process may be used to accurately align and connect atleast one optical element to a wide variety of devices and objects otherthan optoelectronic devices. The optical element may comprise a lensletarray, diffractive optic array or an optical fiber. For example, theprocess may be used to connect an optical element to amicro-electromechanical system (“MEMS”) or a biological or chemicalsample held on a substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is perspective view of an embodiment of the invention.

FIG. 2 shows a perspective view of an embodiment of the inventionmounted on the edge of a circuit board.

FIGS. 3 a-3 b are diagrams of cut-away-side views of the flexibleprinted circuit board, according to an embodiment of the invention.

FIG. 4 is a diagram of an embodiment of the optical power controlsystem, according to an embodiment of the invention.

FIGS. 5 a-5 d are diagrams of different optical beam patterns on anaperture of a photo-detector, according to an embodiment of theinvention.

FIGS. 6 a-6 b are diagrams of alternative embodiments of the opticalpower control system, according to an embodiment of the invention.

FIGS. 7 a-7 b are cut-away-side views showing embodiments of a headregion of the flexible printed circuit board, according to embodimentsof the invention.

FIG. 8 is side view showing an alternative embodiment of a first ferruleand the head region of the flexible printed circuit board, according toan embodiment of the invention.

FIG. 9 is an exploded view of an embodiment of the housing, anembodiment of the first ferrule, an embodiment of a circuit boardmounting structure and an embodiment of the flexible printed circuitboard, according to an embodiment of the invention.

FIG. 10 is a three-dimensional view of an embodiment of the housing,according to an embodiment of the invention.

FIGS. 11 a-11 b are diagrams of an embodiment of an apparatus forholding an optical element, according to an embodiment of the invention.

FIGS. 12 a-12 d show views of images of optoelectronic devices andimages of optical fibers under the high magnification of a split-fieldmicroscope.

FIG. 13 shows the display on a monitor of a video image measuringsystem.

DETAILED DESCRIPTION

I. Introduction

The following embodiments will be described in the context of an opticaltransceiver, receiver or transceiver module and a method of making thesame. Those skilled in the art, however, will recognize that thedisclosed methods and structures are adaptable for broader applications.If the same reference numeral is repeated with respect to differentfigures, it refers to the corresponding structure in each figure.

With reference to FIG. 1, an optical transmitter, receiver ortransceiver module 100 is depicted, according to an embodiment of theinvention. The optical module 100 comprises a flexible printed circuitboard 102 that wraps around and attaches to a circuit board mountingstructure 104. The flexible printed circuit board 102 functions tosupport the electrical components of the optical module 100, such as anarray of optoelectronic devices 106, a driver or amplifier chip 108, anda photo-detector 110. A first ferrule 112, packaging an array of opticalfibers 114, is mounted on top of the array of optoelectronic devices 106in such a manner that one or more of the optical fibers in the array isoptically aligned to one or more of the optoelectronic devices.

Prior to mounting the first ferrule 112 on the array of optoelectronicdevices 106, a first adhesive 116 is dispensed on a top surface of thearray of optoelectronic devices 106. The first adhesive 116 functions tomaintain the precise axial alignment between the array of optical fibers114 and array of optoelectronic devices 106. The first adhesive 116 alsofunctions to produce a high, optical coupling efficiency between theoptical fibers 114 and optoelectronic devices 106. Additionally, thefirst adhesive 116 functions to mechanically stabilize the first ferrule112 to the optoelectronic devices 106.

To further mechanically stabilize the first ferrule 112 to the flexibleprinted circuit board 102, a dam 120 may be formed on the flexibleprinted circuit board 102 and filled with a second adhesive 122. Anhousing 124 is attached to the circuit board mounting structure 104,surrounding and enclosing the first ferrule 112 that is connected to theflexible printed circuit board 102.

In an illustrative embodiment, an optical transmitter or receiver module100 is mounted on a second circuit board 202, as depicted in FIG. 2. Theoptical module, however, does not have to be mounted at the board'sedge. The optical module may b e mounted anywhere on the circuit boardso long as there is room for connecting the optical module to theexternal environment. In operation, the optical module 100 is connectedto the external environment by connecting a fiber optic cable 204 to theoptical module 100. This is accomplished by plugging a second ferrule206 that is attached to one end of a fiber optic cable 204 into theoptical module 100. Once the second ferrule 206 is plugged into theoptical module 100, the module 100 is optically connected to the fiberoptic cable 204. Accordingly, if the optical module 100 functions as atransmitter, the optical module 100 receives electrical signals from thesecond circuit board 202, converts the electrical signals into opticalsignals, and transmits the optical signals into the fiber optic cable204. On the other hand, if the optical module 100 functions as areceiver, the optical module 100 receives optical signals from the fiberoptic cable 204, converts the optical signals into electrical signalsand transmits the electrical signals to the second circuit board 202.

II. Flexible Printed Circuit Board

The flexible printed circuit board 102 is now described in furtherdetail. Specifically, FIG. 3 a is a cut-away-side view of an embodimentof the flexible printed circuit board 102. The flexible printed circuitboard may be bent or folded in any direction, and another embodiment ofthe flexible printed circuit board is shown in FIG. 3 b. The flexibleprinted circuit board 102 is thin, rectangular and flexible with variousedge contours, and it is composed of flexible metal layers that aresandwiched between insulating layers. The entire flexible printedcircuit board may be composed of this multi-layered structure. Inaddition to supporting the electrical components and circuitry of theoptical module 100, the flexible printed circuit board 102 also providesstress relief when connecting the optical module 100 to an externalsource and aids in maintaining the precise alignment of theoptoelectronic devices 106 with an the optical fibers 114.

The flexible printed circuit board 102 is bent in the “Y” direction toform a head region 302, a buckle region 304 and a main body region 306.The head region 302 may function to support the key electricalcomponents and other elements of the optical module 100, such as theoptoelectronic devices 106 and driver or amplifier chip 108. The mainbody region houses a plurality of electronic components 308 and aplurality of electronic circuitry of the optical module 100. The buckleregion 304 is that area of the flexible printed circuit board 102 thatconnects the head region 302 to the main body region 306.

Each region of the flexible printed circuit board is described in detailbelow.

A. Head Region

The head region 302 of the flexible printed circuit board 102 is nowdescribed in detail, and it is shown in FIG. 3 a or FIG. 3 b. The headregion 302 is composed of the same multi-layered structure as the otherregions of the flexible printed circuit board 102. The head region 302is orientated in the “Y” direction, and the head region 302 may be on aplane that is substantially perpendicular to the main body region 306 ofthe flexible printed circuit board 102, as shown in FIG. 3 a or FIG. 3b.

The head region 302 is orientated in the “Y” direction so that theoptical fibers 114 packaged in the first ferrule 112 are opticallyaligned with the optical fibers 114 packaged in the second ferrule 206.As shown in FIG. 3 a or FIG. 3 b, the head region 302 of the flexibleprinted circuit board 102 may function to support the key electricalcomponents of the optical module 100 such as the driver or amplifierchip 108.

The flexible printed circuit board performs the function of changing theplane on which the signals are received. Specifically, the signals arereceived by the flexible printed circuit board in the “X” direction fromthe first ferrule 112 that is optically connected to the optoelectronicdevices 106, which are adapted to the head region 302 of the flexibleprinted circuit board 102. The signals then flow in substantially the“Y” direction in the head region 302 of the flexible printed circuitboard 102. The signals then change planes, as they pass from the headregion 302 through the buckle region 304 and to the main body region 306of the flexible printed circuit board 102, as shown in FIG. 3 a or FIG.3 b. The signals flow in the “X” direction in the main body region.Advantageously, by changing the plane on which the signals travel, theflexible printed circuit board functions to efficiently communicate withboth the fiber optical cable attached to the optical module and anexternal circuit board upon which the optical module is mounted.

1. Optoelectronic Devices

One board-level component of the head region 302 may be the array ofoptoelectronic devices 106. The array of optoelectronic devices 106 maybe adapted approximately in the center of a first surface 310 and/or thesecond surface 704 of the head region 302) as shown in FIG. 3 a or FIG.3 b. The array of optoelectronic devices 106 may be a one-dimensional,two-dimensional or a multi-dimensional array of optoelectronic devices106.

The array of optoelectronic devices 106 may be various types of devicessuch as edge emitting lasers, light-emitting diodes (“LEDs”), verticalcavity surface emitting lasers (VCSELs), other surface emitting devicesor photo-detectors. The optoelectronic devices 106 may also b eintegrated devices combining one or more de vices such as thecombination of VCSELs and transistors or photo-detectors and transistors(or VCSELs, photo-detectors and transistors). The optoelectronic devices106 may also be a heterogeneous array where some of the array elementsare emitters and some are detectors.

If the optoelectronic devices 106 ar e VCSELs, the opt ical module 100functions as a transmitter, sending optical signals into the array ofoptical fibers 114 that are packaged in the ferrule.

If the optoelectronic devices 106 are photo-detectors formed on asemiconductor chip, the optical module 100 functions as a receiver forreceiving optical signals from the array of optical fibers 114 packagedin the first ferrule 112.

In an embodiment, the optoelectronic devices 106 are oxide-confinedVCSELs. Advantageously, oxide-confined VCSELs operate at higher speedsand have lower threshold currents than n on-oxide VCSELs, such asion-implant VCSELs. Additionally, oxide-confined VCSELs are stableVCSELs, exhibiting uniform power and wavelength performance over varyingtemperature ranges. This advantageously would allow the module toperform for longer a duration and high degree of accuracy. Moreover, itis contemplated that use of oxide VCSELs would obviate the need for afeedback loop, as hereafter described. Moreover, oxide-confined VCSELsallow the fabrication of highly uniform arrays, enabling multi-channel,parallel optic applications.

Lastly in another embodiment, a micro-electromechanical system (“MEMS”)array, a micro-pipette array or a biological or chemical sample held ona substrate may be used in place of the array of optoelectronic devices106.

2. Driver or Amplifier Chip

Another board-level component of the head region 302 of the flexibleprinted circuit board 102 may be the driver or amplifier chip 108, asshown in FIG. 3 a or FIG. 3 b. Specifically, a driver or amplifier chip108 may be adapted next to the array of optoelectronic devices 106 onthe first surface 310 and or the second surface 704 of the head region302 of the flexible printed circuit board 102, as shown in FIG. 3 a orFIG. 3 b. In another embodiment, the driver or amplifier chip 108 may beadapted to the main body region of the flexible printed circuit board.

Where the optoelectronic devices 106 are VCSELs, a driver chip is used,and it functions to drive and modulate the VCSELs. Where theoptoelectronic devices 106 are photo-detectors, then an amplifier chipis used, and it amplifies the electronic signals received fromphoto-detectors. Wire bonds 312 or any other suitable means such asplating, welding, tape-automated bonding or the use of flip-chiptechnology may be used to connect the driver or amplifier chip 108 tothe optoelectronic devices 106, as shown in FIG. 3 a or FIG. 3 b. Thedriver or amplifier chip 108 may be monolithically formed on asemiconductor chip or integrated with the array of optoelectronicdevices 106 as a hybrid circuit.

3. Optical Power Control System

Still another board-level component of the head region 302 of theflexible printed circuit board 102 may be an optical power controlsystem. During operation, temperature changes across an array of VCSELsand other factors can cause the power and wavelength of the VCSEL arrayto change. The optical power control system functions to stabilize theperformance of the array of VCSELs over changing conditions.Specifically, if the array of optoelectronic devices 106 aretransmitters such as VCSELs, an optical power control system is adaptedproximate to the array of optoelectronic devices 106 on the firstsurface 310 of the head region 302 of the flexible printed circuit board102.

FIG. 4 is an embodiment of the optical power control system. The opticalpower control system utilizes the photo-detector 110 (or alternatively alight-pipe) to measure the optical output power of a VCSEL in an arrayof VCSELs. In an embodiment of the invention, if the optoelectronicdevices 106 are VCSELs, the optical power control system measures thepower of a thirteenth VCSEL 404 in the array of VCSELs. However, theoptical power may be measured by any other suitable VCSEL in the arrayof VCSELs. The photo-detector's measurement is used to adjust theelectrical power input to each individual VCSEL. This is accomplished bya feedback loop between the photo-detector 110 and the driver chip 108.The driver chip 108 adjusts the laser injection current in response tothe feedback, and this results in a stable array of optoelectronicdevices.

FIGS. 5 a-5 d are diagrams of different optical beam patterns onapertures of photo-detectors. A critical aspect of a robust opticalpower control system is the tracking ratio. The tracking ratio is theability of the photo-detector 110 to track and capture the optical beam408 so that the photo-detector 110 accurately measures the amount ofpower emitted by the VCSEL array. In the ideal situation, the opticalbeam 408 is fully captured by the photo-detector's aperture 502 as shownin FIG. 5 a. This allows the photo-detector 110 to precisely measure thepower of the beam. However, temperature changes, aging, and otherfactors during operation can cause the optical beam 408 to becomemisaligned, as shown in FIG. 5 b. Since the photo-detector's aperture502 captures less of the optical beam 408, the photo-detector is unableto accurately measure the beam's power. This causes the optical powercontrol system to improperly adjust the power of the VCSEL array.Similarly as shown in FIG. 5 c, changes in laser injection current andother factors can create a diverged or enlarged optical beam 504. Again,the photo-detector's aperture 502 detects less power, causing inaccurateadjustments to the power output of the VCSEL array.

Advantageously, the present invention improves the tracking ratio underchanging conditions. The present invention accomplishes this task byadapting a reflector/scatterer 410 to a second end of the first ferrule320, as shown in FIG. 4. An optical path may be created from thethirteenth VCSEL 404 to the reflector/scatterer 410 and onto thephoto-detector 110. The geometry and surface roughness of thereflector/scatterer 410 produces a beam pattern 506 that is highlyuniform, scattered and larger than the photo-detector's aperture, asshown in FIG. 5 d. This uniform and scattered beam pattern 506 has ahigh tolerance for alignment and divergence changes. Accordingly, it isless sensitive to temperature changes, to aging and other issues.Advantageously, this allows the photo-detector 110 to accurately measurethe power of the optical beam 408 under varying conditions andenvironmental circumstances. For example, temperature changes across theVCSEL array may change the optical beam's pattern, alignment anddivergence, and this impacts the photo-detector's 110 ability toaccurately measure power. However, the highly scattered and uniform beampattern produced by the reflector/scatterer 410 is significantly lesssensitive to temperature changes. This allows the photo-detector 110 tocapture the optical beam 504 and accurately measure power. The novelbeam pattern produced by the unique reflector/scatterer 410 allows theoptical power control system to maintain constant power across the VCSELarray under changing conditions. Consequently, the optical power controlsystem produces a stable and uniform VCSEL array.

In an embodiment, the reflector/scatterer 410 is a conical hole that iscoated with a reflecting/scattering coating. The reflective/scatteringcoating may be gold, titanium, aluminum or other types materials thathave the effect of both reflecting and scattering light. Thereflector/scatterer 410 may also be an arbitrarily shaped rough surface,sphere, notch, prism or optical element.

An alternative embodiment of the optical power control system is show inFIG. 6 a. A glob top of optical resin 602 is coated with a reflectivescatterer and is dispensed on the top surface of the array ofoptoelectronic devices 106 and a top surface of the photo detector 606.The glob top 602 scatters light in multiple directions, and a portion ofthe light is detected by the photo-detector 110. The shape and coatingof the glob top 602 may be engineered to provide varying amounts ofscattering for more uniformity and reflection and thus higher energytransfer. As shown by dashed lines in FIG. 6 a, a notch may be cut inthe first ferrule 112 to allow room for the glob top of optical resign.

Another embodiment of the optical power control system is show in FIG. 6b. Here, a reflector 608 is formed separately and then adapted to thetop surface of the array of optoelectronic devices 106 and to the topsurface of the photo detector 606. Similar to the glob top 602, thereflector 608 scatters light in multiple directions, and a portion ofthe light is detected by the photo-detector 110. The shape and coatingof the reflector 608 may be engineered to provide varying amounts ofscattering for more uniformity and reflecting and thus higher energytransfer. The reflector may be in the shape of an ellipsoid,three-dimensional conical hole or other shape. It also may be ageometrically-shaped object. In another embodiment, the reflector isadapted to the second end 320 of the first ferrule 112 rather thanadapted to the top surface of array of optoelectronic devices 106 andphoto detector 606. As shown by dashed lines in FIG. 6 a, a notch may becut in the ferrule to allow room for the glob top of optical resign.

4. Spacer

An additional board-level component of the head region 302 of theflexible printed circuit board 102 may be a spacer 314, as shown in FIG.3 a or FIG. 3 b. The spacer 314 may be shaped like a square and may becomposed of silicon material. A bottom surface of the spacer 314 may beadapted approximately in the center of the head region 302, as shown inFIG. 3 a or FIG. 3 b. A top surface of the spacer 314 may serve as amounting surface for the array of optoelectronic devices 106 when theyfunction as receivers (e.g., photo-detectors). The spacer 314 isoptional if the optoelectronic devices 106 function as emitters (e.g.,VCSELs). The spacer also may function as a mounting surface for othercomponents such as the first ferrule 112.

The spacer 314 may function to raise the height of the array ofoptoelectronic devices 106 so as to maximize the optical couplingbetween the optoelectronic devices 106 and the optical fibers 114, whichare packaged in the first ferrule 112. The spacer may function to adjustthe length of the wire bonds or other electrical connection meansbetween the array of optoelectronic devices 106 and other componentssuch as the driver or amplifier chip 108. The spacer also may be used toaid in creating a gap between the array of optoelectronic devices 106and the array of opt ical fibers that are inside the first ferrule 114.

The spacer 314 also may function to raise the height of the array ofoptoelectronic devices 106 so that a top surface of the array ofoptoelectronic devices 106 is approximately on the same plane as theother components, such as the driver or amplifier chip 108, that areadapted on t he head region 302, as shown in FIG. 3 a or FIG. 3 b.Advantageously, by maintaining the optoelectronic devices on the sameplane as the other electrical components, the wire bonds 312 between thecomponents on the head region 302 more robust and efficient.

The spacer 314 may be optional if the optoelectronic devices 102 havesufficient height so as to place the second end of the first ferrule 320at an optimal position above the top surface of the driver or amplifierchip 108. According to a preferred embodiment, a small interstitialspace or gap is maintained between the second end of the first ferrule320 and the top surface of the optoelectronic devices 102. Inalternative embodiments, this interstitial gap may be omitted.

In another embodiment, the spacer 314 also may function to create orform a gap between the array of optoelectronic devices 106 and the arrayof optical fibers. Specifically, the spacer 314 may be adjacent to thearray of optoelectronic devices. The top surface of the spacer 314 maybe higher than the top surface of the array of optoelectronic devices106. The top surface of the spacer may be in contact with the second endof the first ferrule 320. Accordingly, this creates or forms a gapbetween the optoelectronic devices and array of optical fibers packagedin the first ferrule.

5. Optoelectronic Mounting Structure

The electrical components on the flexible printed circuit board 102generate heat, and an optoelectronic mounting structure 702 may be usedto transmit this heat to the circuit board mounting structure 104, asexplained below.

FIG. 7 a is a cut-away-side view showing an alternative embodiment ofthe head region 302 of the flexible printed circuit board 102, accordingto an embodiment of the invention. Specifically, the optoelectronicmounting structure 702 has a first surface 710 and a second surface 712.The first surface 710 of the optoelectronic mounting structure 702passes along a second surface 704 of the head region 302 of the flexibleprinted circuit board 102. The second surface 712 of the optoelectronicmounting structure 702 is adapted to an upper surface 708 of the circuitboard mounting structure 104 with a compliant adhesive. Theoptoelectronic mounting structure may be copper or a similar conductivematerial. The optoelectronic mounting structure may be coated with goldor other adhesion promotion layers such as nickel. An window 706 may beformed in the head region 302 of the flexible printed circuit board 102so as to provide access to the optoelectronic mounting structure 702.The array of optoelectronic devices 106 may be mounted in the window 706directly on top of the optoelectronic mounting structure 702.Accordingly, the optoelectronic mounting structure provides a thermaland an electrical contact area for the optoelectronic devices. Otherelectrical components, such as the driver or amplifier chip 108 also maybe mounted in the window 706 directly on the optoelectronic mountingstructure 702.

The optoelectronic mounting structure advantageously 702 dissipates heatgenerated by the array of optoelectronic devices 106 and otherelectrical components by spreading the heat and efficiently transmittingit to the circuit board mounting structure 104. The optoelectronicmounting structure 702 also provides an electrical contact path to theoptoelectronic devices 106 since the back side of the optoelectronicdevices 106 may be gold or copper plated and may be mounted directly toa copper optoelectronic mounting structure 702. Moreover, since theoptoelectronic mounting structure 702 may be a solid copper plane, itmay acts to limit electromagnetic interference. Acting as a ground planefor the optoelectronic devices 106, the optoelectronic mountingstructure 702 provides electrical shielding by containing any electricalfields that may exist so that the electrical fields do not radiate andcreate cross talk. The optoelectronic mounting structure 702additionally may provide a stable mounting surface for theoptoelectronic devices 106, and it may function to raise or change theheight of the electrical components. The optoelectronic mountingstructure 702 also provides mechanical rigidity to the head region 302of the flexible printed circuit board 102. This mechanical rigiditystiffens the head region 302 and advantageously aids in the assemblyprocess.

FIG. 7 b is a cut-away-side view showing an alternative embodiment ofthe head region 302 of the flexible printed circuit board 102, accordingto an embodiment of the invention. Specifically, openings 714 in thehead region 302 of the flexible printed circuit 102 board may functionto dissipate heat to the optoelectronic mounting structure 702. Theopenings 714 may be heat pipes, thermal vias or similar structures thattransmit heat. The openings 714 may be formed in the head region 302 soas to provide access to the optoelectronic mounting structure 702.Electrical components, such as the array of optoelectronic devices 106and the driver or amplifier chip 108, may be mounted on the firstsurface of the head region 302. Heat generated by these electricalcomponents may pass through the openings 714 and to the optoelectronicmounting structure 702. The optoelectronic mounting structure 702dissipates or spreads this heat to the circuit board mounting structure104.

6. Ferrule

The optical module 100 may include the first ferrule 112, as shown inFIG. 3 a or FIG. 3 b. The first ferrule is mounted on the head region302 of the flexible printed circuit board 102. More specifically, thesecond end of the first ferrule 320 is mounted on the top surface of thearray of optoelectronic devices 106. The first ferrule 112 is preciselyaligned and attached directly above the active region of the array ofoptoelectronic devices 106 so that a high coupling efficiency (low lossof light) is achieved. In other words, each optical fiber 114 in thefirst ferrule 112 is accurately aligned to a corresponding individualoptoelectronic device 106 so that the array of optical fibers 114 insidethe first ferrule 112 is optically aligned with the array ofoptoelectronic devices 106. The precise alignment and attachment of thefirst ferrule 112 to the array of optoelectronic devices 106 isaccomplished by using highly precise machinery and adhesive, and thisnovel process is explained below.

The first ferrule 112 may comprise a rectangular ferrule. The firstferrule 112 packages an array of optical fibers 114, extending from afirst end 318 of the first ferrule 112 to a second end 320 of the firstferrule 112. Two alignment pins 316 may be adapted to the first end 318of the first ferrule 112. The alignment pins function to mate the firstferrule 112 to a second ferrule 206. Alternatively, two alignment pinholes may be adapted to the first end 318 of the first ferrule 112 inplace of the two alignment pins 318. The alignment pin holes function tomate the first ferrule 112 to a second ferrule 206.

FIG. 8 is a side-view showing an alternative embodiment of the firstferrule 112 and the head region 302 of the flexible printed circuitboard 102, according to an embodiment of the invention. Costs arereduced by using a smaller optoelectronic device 106, as shown in FIG.8. A notch 802 exists at the second end of the first ferrule 320 so thatthere is sufficient room for wire bonding between the optoelectronicdevices 106 and driver or amplifier chip 108. Advantageously, the notch802 allows positioning the driver chip or amplifier chip 108 in closeproximity to the smaller optoelectronic devices 106. Therefore, thenotch 802 obviates the need for long wire bonds to connect theoptoelectronic devices to the driver or amplifier chip.

In another embodiment, an array of optical elements may be used in placeof the array of optical fibers 114. The optical element may comprise alenslet array, diffractive optic array, a lens, filter, pipette,capillary tube or optical fibers. Also, the optical element does nothave to be optical as, for example, in embodiments of the presentinvention in which biological or chemical analysis is performed. Theoptical element array may be a one-dimensional, two-dimensional ormulti-dimensional array of optical elements.

In contrast to a single optical element or fiber, an array of opticalelements or fibers introduces engineering, design, assembly andpackaging complexity. This complexity was taken into account inembodiments of the invention. For example, an array of optical elementsgenerates more heat and electromagnetic interference that a singleoptical element, and this must be considered in all aspects of makingand using the device. Also, unlike aligning a single optical element toan optoelectronic device, aligning an array of optical elements to anarray of optoelectronic devices is considerably more difficult andcomplex. Moreover, an array of optical elements can more readily becomeeffected by electrical or optical cross-talk since the optical elementsare closely coupled. Therefore, the array is highly subject to signaldegradation, and design limitations must be made to take these factorsinto account. Additionally, working with an array rather than a singleoptical fiber requires developing new tools and techniques for variousmanufacturing aspects such as precision alignment and eye-safety. Suchtools and techniques were developed specifically for embodiments of thisinvention. In summary, for these and other reasons, an array of opticalelements introduces engineering, design, assembly and packagingcomplexity that is simply not present with a signal optical element, andthis added complexity was taken into account in embodiments of theinvention.

7. First Adhesive

Prior to mounting the first ferrule 112 on top of the array ofoptoelectronic devices 106, a first adhesive 116 is dispensed on the topsurface of the array of optoelectronic devices 106, as shown in FIG. 3 aor FIG. 3 b. The first adhesive is preferably an optically clearadhesive or a gel that has a complementary index of refraction to theoptical fibers 114.

The first ferrule 112 is held suspended above the top surface of thearray of optoelectronic devices 106 in the first adhesive 116. Theoptical adhesive 116 may be cured with UV light, RF radiation, air,microwave radiation or thermal means, depending on the type of adhesivethat is used. Once the optical adhesive 116 is cured, the space or gapbetween the second end of the first ferrule 320 and the top surface ofthe optoelectronic devices 118 is preserved or set; this space havingbeen filled with the first adhesive 116. In other words, a thin layer offirst adhesive 116 exists at the interface between the second end of thefirst ferrule 320 and the top surface of the optoelectronic devices 118.

The first adhesive 116 functions to stabilize and hold the first ferrule112 to the array of optoelectronic devices 106. The first adhesive 116maintains the precise alignment of the array of optical fibers 114packaged in the first ferrule 112 to the array of optoelectronic devices106. The first adhesive also functions to maintain the gap that existsbetween the first ferrule 112 and array of optoelectronic devices 106.

Advantageously, the first adhesive 116 produces a high couplingefficiency between the array of optical fibers 114 packaged in the firstferrule 112 and the array of optoelectronic devices 106. Specifically,the first adhesive 116 is an optically clear adhesive or gel and hasalmost the same refractive index as the optical fibers. Accordingly, byproviding a refractive index match to the optical fibers, light passingfrom the array of optoelectronic devices 106 to the array of firstfibers 114 (or vice versa) experiences minimal Fresnel reflection lossand optical divergence over the gap distance that exists between thearray of optoelectronic devices 106 and the array of first fibers 114.This produces a high-coupling efficiency at the interface between thetop surface of the optoelectronic devices 106 and the optical fibers114. The first adhesive 116 also serves to prevent air from existing atthe interface or space between the first ferrule 112 and the array ofoptoelectronic devices 106. The elimination of air at the interface orgap is desirable because air has a lower refractive index than theoptoelectronic devices 106, the optical fibers 114 and the firstadhesive 116. The refractive index difference introduces reflectionlosses, and the lower reflective index results in greater beamdivergence per unit propagation length. If air were present, lightpassing from the optoelectronic devices 106 to the optical fibers 114(or vice versa) may experience greater divergence, thereby reducing theefficiency of the coupling. Furthermore, the first adhesive prevents asecond adhesive 122 from inadvertently seeping or wicking into the gapor space between the bottom surface of the ferrule and the top surfaceof the optoelectronic devices. Consequently, the first adhesive 116advantageously produces a high-coupling efficiency between theoptoelectronic devices 106 and the optical fibers 114 that are packagedin the first ferrule 112.

The first adhesive 116 not only enhances the coupling efficiency betweenthe optical fibers 114 and optoelectronic devices 106 by providing arefractive index match to the optical radiation, but it also servesanother important purpose. Specifically, the first adhesive 116 providesmechanical robustness by securing the first ferrule 112 to the array ofoptoelectronic devices 106. As previously stated, the gap or spacebetween the bottom surface of the first ferrule 112 and the top surfaceof the optoelectronic devices 118 is filled with the first adhesive. Thefirst adhesive functions to mechanically stabilize the first ferrule 112to the head region 302 of the flexible printed circuit board 102. Thefirst adhesive 116 provides support for any lateral, axial or rotationalstrain that may be created when a fiber optic cable is attached to theoptical module. Furthermore, this allows proceeding to the dam andwell-fill step, which is explained below, with minimal or no supportingstructure to maintain the precision axial alignment of the array ofoptical fibers 114 packaged in the first ferrule 112 to the array ofoptoelectronic devices 106. Accordingly, the first adhesive 116advantageously reduces manufacturing time and costs by providingmechanical robustness in addition to providing high coupling efficiency.

8. Second Adhesive and Dam

As previously stated, the first adhesive mechanically stabilizes thefirst ferrule 112 to the head region 302 of the flexible printed circuitboard 102. In another embodiment, a second adhesive 122 may be adaptedto the head region 302 to further mechanically stabilizes the firstferrule 112 to the head region 302 of the flexible printed circuit board102, as shown in FIG. 3 a or FIG. 3 b. Similar to the first adhesive116, the second adhesive 122 may provide support for any lateral, axialor rotational strain that may be created when a fiber optic cable isattached to the optical module. No dam is necessary to form the firstadhesive 116.

To further mechanically stabilize the first ferrule 112 to the headregion, a darn 120 may be formed on the head region 302 and filled withthe second adhesive 122, as shown in FIG. 3 a or FIG. 3 b. The secondadhesive, however, may be used without the dam. The dam may beconstructed or dispensed, and the dam 120 may be dispensed and formed ina single or multi-layered path. The dam 120 may be in the shape of asquare, diamond, oval or any other shape that effectively stabilizes andencloses the optoelectronic devices and possibly wire bonds and otherdie on the head region 302 of the flexible printed circuit board 102.The dam 120 may furthermore surround and enclose all of the componentson the head region 302 for extra protection. The dam 120 may beconstructed and formed on the first surface 310 of the head region 302of the flexible printed circuit board 102.

The dam 120 may surround the first ferrule 112, driver or amplifier chip108 or other electrical components, as shown in FIG. 3 a or FIG. 3 b.The dam 120 may be composed of adhesive or epoxy. The dam 120 may beformed or built by dispensing several layers of adhesive or epoxy on topof each other over time until the desired height and width of the dam120 is achieved. The adhesive or epoxy may be any standard well-fill orpotting epoxy. Alternatively, as previously stated, the dam may bedispensed and formed in a single path.

The area within the darn may be filled with the second adhesive 122. Thesecond adhesive 122 preferably covers the driver or amplifier chip 108,array of optoelectronic devices 106, and any other electrical componentsthat are adapted to the head region 302, as shown in FIG. 3 a or FIG. 3b. A sufficient amount of second adhesive 122 is poured inside the darnarea so that the height of the second adhesive 122 may span from thefirst surface 310 of the head region 302 of the flexible printed circuitboard 102 to somewhere below the first end 318 of the first ferrule 112,as shown in FIG. 3 a or FIG. 3 b. After the second adhesive 122 has beencured, the dam 120 and second adhesive 122 function to mechanicallystabilize the first ferrule 112 to the first surface 310 of the headregion 302 of the flexible printed circuit board 102.

Advantageously, the dam 120 and second adhesive 122 may provideadditional mechanical support to further stabilize the first ferrule 112to the head region 302 of the flexible printed circuit board 102. Thedam 120 and second adhesive 122 may function to absorb stress andprovide rigidity and strength that may be needed when connecting theoptical module to an external environment such as a fiber optic cable.Also, the dam 120 and second adhesive 122 may prevent movement that mayoccur over temperature variances. Moreover, the dam 120 and secondadhesive 122 may function to provide moisture blocking and protection tothe electrical components and circuitry adapted to the first surface 310of the head region 302 of the flexible printed circuit board 102.

9. Third Layer

For airtight sealing of the optical module, the surface area of thesecond adhesive 122 may be covered with a third layer. The third layermay protect the optical module by blocking the permeation of moistureand providing electric shielding. The third layer may be a conductiveand or moisture blocking adhesive such as gel silicon resin. It may alsobe a metallic, dielectric or other type of coating that providesnecessary protection to the optical module.

10. Attenuator or Conditioner

In an embodiment of the invention, an attenuator may be used thatfunctions to modify the performance of the array of optoelectronicdevices. Specifically, superior performance of the array ofoptoelectronic devices typically is found if such devices are operatedat the mid-point rather than low-point of their power range. However,operating the optoelectronic devices at the mid-point of their powerrange may not meet optical output requirements. One solution is tooperate the optoelectronic devices at the mid-point of their power rangebut not transmit all of the power out of the end of the array of opticalfibers. This may be accomplished through the use of the attenuator. Theattenuator may function to reflect, absorb and or scatter the opticaloutput of at least one optoelectronic device. Also, the attenuatoradvantageously may control optical cross-talk, reduce back-reflectionand may eliminate feedback noise.

One embodiment of the attenuator may be a coating on the first or secondend of the first ferrule or a coating on the first or second end of thearray of optical elements that are packaged in the ferrule. It also maycomprise a coating on the first end of the array of optoelectronicdevices. The coating may be a metal, dialetric, organic or othermaterial, and the coating may be patterned. Another embodiment of theattenuator may be a gel-like substance that is deposited in the gap thatexists between the first end of the optoelectronic devices and the firstend of the optical fibers. In this embodiment, the attenuator wouldfunction to absorb some of the light emitted by the optoelectronicdevices. Other embodiments of the attenuator may be increasing theabsorption of the first adhesive, introducing a controlled seeping orwicking of an absorbing second adhesive, changing the gap distance toreduce coupling, changing the refractive index to introduce Fresnelreflection and introduce divergence, changing the lateral alignment, orchanging the surface finish of the optical fibers. Finally, otherembodiments of the attenuator may include changing the opticaltransmission characteristics of the array of optical fibers so that theyabsorb, reflect and or scatter light. In this manner, the optical energyexiting the array of optical fibers will have its signal power reduced.This may be accomplished by changing the surface finish of the cores ofthe optical fibers (e.g., using frosted, wavy or rough surface glass) orby coating the inner surfaces of the fiber optic cores.

Finally, in another embodiment of the invention, a conditioner may beused to improve the performance of the array of optical fibers bychanging the way the optical energy is launched into the optical fibers.For example, conditioning the launch of optical energy can improve theeffective bandwidth of the optical fibers. The conditioner may functionto change the phase distribution of the optical energy that is emittedby the optoelectronic devices.

Conditioning the launch of the optical energy flowing into the opticalfibers from the optoelectronic devices may be accomplished as follows:(1) patterning a coating on the first end of the array of optoelectronicdevices; (2) patterning a coating on the first or second end of thearray of optical fibers; (3) depositing a gel-like substance between thefirst end of the optoelectronic devices and the first end of the opticalfibers; (4) adapting a diffractive object on the input or output of thearray of optical fibers so as to change the structure of the opticalenergy; (5) changing the lateral position of the array of optoelectronicdevices relative to the array of optical fibers; (6) changing theoptical transmission characteristics of the array of optical fibers; (7)tilting the array of optoelectronic devices relative to an optical path;and (8) changing the optical transmission characteristics of the arrayof optical fibers so that they absorb, reflect and or scatter light.These and other methods that are known in the art may be used to improvethe performance of the array of optical fibers by changing the way theoptical energy is launched into the optical fibers.

B. Buckle Region

In addition to the head region 302, the flexible printed circuit board102 also comprises a buckle region 304, which will now be described withreference to FIG. 3 a or FIG. 3 b. The buckle region 304 is that area ofthe flexible printed circuit board 102 connecting the head region 302 tothe main body region 306 of the flexible printed circuit board 102. Thebuckle region 304 is thin and composed of the same multi-layeredstructure as the other regions of the flexible printed circuit board102. A plurality of electrical circuitry may be adapted both to a firstsurface and a second surface of the buckle region 304. The electricalcircuitry functions to electrically connect the head region 302 to themain body region 306 of the flexible printed circuit board 102.

The buckle region functions to absorb any stress and misalignment thatmay occur when the head region 302 and main body region 306 areconnected to the circuit board mounting structure 104 during theassembly process. Specifically, after the head region 302 is attached tothe circuit board mounting structure 104, the flexible printed circuitboard 102 is wrapped or folded around and attached to the circuit boardmounting structure 104, as explained in detail below. Alternatively, themain body region 306 may be first connected to the circuit boardmounting structure 104 followed by folding the flexible printed circuitboard and connecting its head region 302 to the circuit board mountingstructure 104. The housing 124 is then connected to the circuit boardmounting structure 102. The first ferrule 112, which is adapted to andprotrudes from the head region, is then aligned and housed in alongitudinal cavity 1006 of the housing 124. However, stress ormisalignment may occur when connecting the housing 124 to the circuitboard mounting structure 104.

The buckle region 304 functions to absorb any misalignment or stressthat may occur during this assembly process. As shown in FIG. 3 a orFIG. 3 b, the buckle region 304 bends in the “Y” direction. Bending thebuckle region 304 provides the buckle region 304 with bending freedom inthe x, y and z direction, as well as rotational freedom. This bendingfreedom allows the buckle region 304 to absorb any stress that may occurduring the assembly process when aligning and attaching the housing 124to the circuit board mounting structure 104.

C. Main Body Region

In addition to a buckle region 304 and a head region 302, the flexibleprinted circuit board 102 also comprises a main body region 306. Themain body region 306 will now be described with reference to FIG. 3 a orFIG. 3 b. The main body region 306 is thin, rectangular shaped andflexible. The main body region 306 is composed of the same multi-layeredstructure as the other regions of the flexible printed circuit board.The main body region 306 functions to house the other electricalcomponents and circuitry of the optical module 100. The electricalcomponents may serve a variety of functions, including connection of theoptical module to the system to which it is located. Accordingly, aplurality of electrical components 308 and a plurality of electricalcircuitry may be adapted to a first surface 324 and/or a second surface326 of the main body region 306 of the flexible printed circuit board102, as shown in FIG. 3 a or FIG. 3 b.

1. Electrical Connections

A series of electrical connections may be adapted to the first or secondsurface 324 of the main body region 324 of the flexible printed circuitboard 102. The electrical connections function to electrically connectthe flexible printed circuit board to an external environment such asanother circuit board. The electrical connections may comprise ball gridarrays, solder balls, wire leads, land-grid arrays with conductiveinterposers, or any other means to electrically connect the flexibleprinted circuit board to an external environment.

D. Summary

In summary, the flexible printed circuit board 102 supports the mainelectrical components and elements of the optical module, such as theoptoelectronic devices 106, driver or amplifier chip 108 and firstferrule 112, as well as providing bending freedom and stress relief tothe optical module 100. The flexible printed circuit board 102 isattached to, and partially enclosed by, a housing 902, which isdescribed below.

II. Circuit Board Mounting Structure and Housing

FIG. 9 is an exploded view of the flexible printed circuit board 102,first ferrule 112, a circuit board mounting structure 104 and an housing124.

A. Circuit Board Mounting Structure

The circuit board mounting structure 104 functions in part as a mountingstructure for the flexible printed circuit board and as a heat sink todissipate heat generated by the circuit board 102. Specifically, theflexible printed circuit board 102 is bent and wrapped around thecircuit board mounting structure 104. A second surface 904 of theflexible printed circuit board 102 is attached to a bottom surface 914and a first end 910 of the circuit board mounting structure 104, asshown in FIG. 9. Alignment ridges, guide pins or guide pin holes mayexist along the bottom surface 914 and first end 910 of the circuitboard mounting structure, although they are not necessary. The alignmentfeatures assist in aligning and holding the flexible printed circuit 102board to the circuit board mounting structure. A fourth adhesive is usedto firmly attach the flexible printed circuit board 102 to the circuitboard mounting structure 104. The thermal expansion coefficient andcompliance of the fourth adhesive advantageously assists in preventingexpansion or contraction of the circuit board mounting structure fromdamaging the flexible printed circuit board 102. The flexible printedcircuit board 102 bends around the circuit board mounting structure 104in such a manner that the head region 302 of the flexible printedcircuit board 102 is housed inside the first end 910 of the circuitboard mounting structure 104, as shown in FIG. 9. A cavity 912 on thefirst end 910 of the circuit board mounting structure 104 functions tohouse the head region 302 of the flexible printed circuit board 102. Inanother embodiment, there is no cavity 912, as is explained below. Aseries of heat sink ridges adapted to the circuit board mountingstructure function to dissipate heat generated by the flexible printedcircuit board.

In an embodiment as shown in FIG. 7, the second surface 704 of the headregion 302 of the flexible printed circuit board 102 is attached to thefirst surface 710 of the optoelectronic mounting structure 702. Thesecond surface 712 of the optoelectronic mounting structure 702 isattached to the upper surface 708 of the circuit board mountingstructure 104 with a compliant adhesive. The flexible printed circuitboard 102 then wraps around the circuit board mounting structure 104 sothat the remaining portion of the second surface 904 of the flexibleprinted circuit board is attached to the bottom surface 914 of thecircuit board mounting structure 104, as shown in FIG. 9.

As shown in FIG. 9, the circuit board mounting structure has feet 916for connecting the optical module 100 to an external environment such asa second circuit board 202. The feet 916 have ridges that allow aportion of each foot 916 to drop into a hole on the second circuit board202 and therefore attach and align the optical module 100 to the secondcircuit board 202. The ridges on the feet also maintain the opticalmodule 100 at a specified distance above the second circuit board 202.

The circuit board mounting structure 104 has snap slots 906, set screwholes and or alignment pin holes on the first end 910 for connecting thefirst end of the circuit board mounting structure to housing 124, asdiscussed in detail below.

B. Housing

The housing 124 is connected to the circuit board mounting structure104, and the housing 124 will now be described in detail with referenceto FIG. 10. The housing 124 may be made of a non-conductive material.The housing 124 comprises a mating end 1002, as shown in FIG. 10 a, anda receiving end 1004, as shown in FIG. 10 b. A longitudinal cavity 1006extends through the housing 124 from the mating end 1002 to thereceiving end 1004, as shown in FIGS. 10 a-10 b.

The mating end 1002 of the housing 124 has tabs 1008 and alignment pins1010 for connecting the mating end 1002 to the first end 910 of thecircuit board mounting structure 104, as shown in FIG. 10 a. Theposition of the tabs 1008 correspond to the position of the snap slots906 located on the first end 910 of the circuit board mounting structure104. Similarly, the position of the alignment pins 1010 correspond tothe position of the alignment pin holes on the first end 910 of thecircuit board mounting structure 104. (See FIG. 9.) Thus, by simplyengaging the tabs 1008 and alignment pins 1010 on the housing 124 intothe snap slots 906 and alignment pin holes on the circuit board mountingstructure 104, the housing 124 snaps on to the circuit board mountingstructure 104 and is firmly attached: In the above-stated embodiment,the housing is snapped onto the circuit board mounting structure. Inother embodiments, the housing may be connected by using otherattachment methods such as glue, screws or through the use of othermechanical fixtures. Furthermore, inserts may be adapted to the matingend of the housing that function to hold the circuit board mountingstructure to the housing. The inserts aid in applying a force to thetabs that maintain the tabs firmly in place. These inserts may be in theform of wedges, spring-clips, stakes or shims.

Additionally, alignment members on the mating and receiving ends of thehousing function to hold and align the position of the first and secondferrules relative to the position of the housing. These alignmentmembers may be inwardly sloping walls at an opening of the longitudinalcavity. The alignment members act independently or in concert with thealignment pins and tabs to align and connect the first ferrule and thecircuit board mounting structure.

Once the housing 124 is snapped onto the circuit board mountingstructure 104, at least one elastomeric pressure ring 1012 that is inproximity to the housing 124 functions to secure the housing 124 and thehead region 302 of the flexible printed circuit board 102 to the circuitboard mounting structure 104. Specifically, the elastomeric pressurering 1012 may be in a variety of shapes and forms such as a circular,oval spaces or donuts, as shown in FIG. 9. The elastomeric pressure ring1012 has multiple purposes. First, upon connecting the housing 124 tothe circuit board mounting structure 104, the elastomeric pressure ring1012 is compressed, and this compression creates an outward elastomericforce in the direction of the receiving end 1004 of the housing 124 thatmaintains the tabs 1008 and the snap slots 906 in a firmly lockedposition. With the compression force on the tabs 1008 and snap slots906, a high degree of manufacturing tolerances is achieved. Second, thepressure or force created by the compressed ring 1012 aids in bondingthe optoelectronic mounting structure 702 to the circuit board mountingstructure 104. The optoelectronic mounting structure 702 is bonded tothe circuit board mounting structure 104 with adhesive, and the pressureproduced by the compressed ring 1012 holds the optoelectronic mountingstructure 702 firmly against the circuit board mounting structure 104while the adhesive is cured. Accordingly, the elastomeric pressure ring1012 produces tighter bonding between the circuit board mountingstructure 104 and the optoelectronic mounting structure 702. Third, oncethe housing 124 is snapped onto the circuit board mounting structure104, the pressure or force created by the elastomeric pressure ring 1012provides a more robust moisture seal between the housing 124 and thecircuit board mounting structure 104.

Upon attachment of the housing 124 to the circuit board mountingstructure 104, the first ferrule 112 is housed in the longitudinalcavity 1006 of the housing 124, and alignment ridges inside thelongitudinal cavity 1006 engage and hold the first ferrule 112 in place.

In the above-described embodiment as shown in FIGS. 9-10, the housing124 slides into the circuit board mounting structure 104, and the headregion 302 of the flexible printed circuit board 102 is buried in thecavity 912 of the first end 910 of the circuit board mounting structure104. However, in another embodiment, the first end 910 of the circuitboard mounting structure 104 may not have a cavity, and the head region302 may exist on the outside of the first end 910 of the circuit boardmounting structure 104. In this embodiment, instead of having thehousing 124 slide into the circuit board mounting structure 104, thehousing 124 may slide over the circuit board mounting structure 104, andthe head region 302 may be housed in a cavity inside the housing 124. Instill another embodiment, neither the housing 124 nor the circuit boardmounting structure 104 may have a cavity, and the two parts simply maymate with each other.

Finally, in another embodiment of the housing, a metallic coating may beapplied to at least a portion of the mating end 1002 of the housing 124.The metallic coating functions to provide electromagnetic shielding. Inyet another embodiment, the housing may be made out of multiplematerials and at least one of those materials would function to provideelectromagnetic shielding.

C. Attachment of Fiber Optic Cable

Finally, as shown in FIG. 10 b, the receiving end 1004 of the housing124 functions to connect the optical module 100 to an external system.The receiving end 1004 receives a second ferrule 206, which is typicallyattached to one end of a fiber optic cable 204. The second ferrule mateswith the first ferrule, as described below. The second ferrule 206 maybe a MT type connector, MU type connector, MPO type connector or othertype connectors.

In operation, the second ferrule 206 is inserted into the receiving end1004 of the to housing 124. Wings 1014, snaps or beams on the receivingend 1004 align, grab and hold the second ferrule 206, and the wings 1014snap onto the second ferrule 206. The wings 1014 function to providealignment compliance when connecting the second ferrule 206 to thehousing 124. Moreover, the wings 1014 are flexible and may absorb anystress that may arise due to movement of the cable 204 that is attachedto the second ferrule 206. The wings 1014 further provide a holdingforce that aids in holding the second ferrule 206 to the first ferrule112. Alignment ridges inside the longitudinal cavity 1006 of the housing124 further engage and hold the second ferrule 206 in place.

Once inside the longitudinal cavity 1006, the second ferrule 206 mateswith the first ferrule 112 that is also housed in the longitudinalcavity 1006 of the housing 124. The second ferrule 206 mates with thefirst ferrule 112 by engaging the alignment pins 316 located on thefirst end 318 of the first ferrule 112 with alignment pin holes locatedon a mating end of the second ferrule 206. The alignment pins 316 andalignment pin holes function to provide fine alignment between themating arrays of optical fibers that are packaged within the matingferrules. Alternatively, the first ferrule may have alignment holes andthe second ferrule may have alignment pins, and the ferrules wouldaccordingly mate in a similar fashion.

Once the ferrules are mated, the array of optical fibers that arepackaged in the ferrules are axially aligned, and the ferrules areoptically connected. For example, if the optical module 100 functions asa receiver, optical signals pass from the fiber optic cable 204, throughthe optical fibers packaged in the ferrules 206 and 112 and to theoptoelectronic devices 106, which are mounted on the flexible printedcircuit board 102. The optical module 100 converts the optical signalsinto electrical signals and transmits these signals to an externalenvironment, such as a printed circuit board, for processing.

III. Alignment and Attachment Process

A. Overview

An important aspect of an embodiment of the invention is the precisealignment and attachment of the first ferrule 112 to the array ofoptoelectronic devices 106 that are mounted on the flexible printedcircuit board 102. A process, according to an embodiment of the adinvention, for aligning and connecting the first ferrule 112 to thearray of optoelectronic devices 106 comprises the following steps:

-   -   1. Holding the first ferrule 112 directly above the        optoelectronic devices 106;    -   2. Aligning the array of optical fibers 114 packaged in the        first ferrule 112 with the array of optoelectronic devices 106        so that each optical fiber is optically aligned to a        corresponding individual optoelectronic device;    -   3. Depositing the first adhesive 116 on a top surface of the        array of optoelectronic devices 106;    -   4. Placing the first ferrule 112 on top of the first adhesive        116;    -   5. Tacking and curing the first adhesive 116 as to mechanically        stabilize the first ferrule 112; and    -   6. Forming a dam 120 around the first ferrule 112 on the        flexible printed circuit board 102, dispensing the second        adhesive 122 inside the dam area, and curing the first adhesive        122.

These precision alignment and attachment steps are discussed below.

A high-precision alignment machine may be used in combination with aseries of other apparatuses to produce precise alignment and attachmentof optical fibers to optoelectronic devices. These machines combine manycritical technologies to perform alignment with a lowcost manufacturingenvironment. These technologies include: (1) a high-precision stage thatis used to hold the flexible printed circuit board 102; (2) ahigh-precision alignment arm for accurately placing the first ferrule112 on the optoelectronic devices 106 that are adapted to the flexibleprinted circuit board 102; (3) a top-down view camera; (4) side-viewcamera; (5) video monitors; (6) split-field microscope; and (7) opticalvideo system function together to replace the labor-intensiveactive-alignment process. Alternatively, computers and software mayperform many of above-stated technologies. An example of one of the manyprocess that may be used with this equipment is explained in thefollowing paragraphs.

B. An Apparatus For Holding an Optical Element

The first step in the precise alignment and attachment of the firstferrule 112 to the array of optoelectronic devices 106 is to hold thefirst ferrule 112 at the end of a high-precision stage. This isaccomplished through the use of an apparatus for holding an opticalelement, as explained in this section.

FIGS. 11 a-11 b show views of an embodiment of the apparatus for holdingan optical at element. The apparatus for holding an optical element 1100holds the first ferrule 112 through the use of pin-positioning holes1102 and vacuum pressure. The apparatus for holding an optical elementhas a first end 1112 and a second end 1114. The apparatus for holding anoptical element 1100 may have two pin-positioning holes 1102 on a bottomsurface 1104 of the second end 1114 for receiving the alignment pins 316of the first ferrule 112, as shown in FIGS. 11 a-11 b. As shown in FIG.11 b, an array of optical fibers 1106 may be packaged between thepin-positioning holes 1102, and it is optically aligned with the arrayof optical fibers 114 that are packaged in the first ferrule 112. Theinnermost optical fibers in the apparatus for holding an optical element1100 are milled out, forming a longitudinal cavity 1108 running throughthe apparatus for holding an optical element 1100 from the first end1112 to the second end 1114, as shown FIG. 11 b. A vacuum is placed at atop surface of the first end 1112 of the longitudinal cavity 1108, andthe longitudinal cavity 1108 functions as a vacuum slot. Accordingly,once the alignment pins 316 from the first ferrule 112 are mated withthe pin-positioning holes 1102 on the apparatus for holding an opticalelement 1100, the vacuum slot functions as a vacuum clamp, holding thefirst ferrule 112 in place. Alternatively, an electrostatic clamp may beused in place of the vacuum clamp. Also, another embodiment may comprisealignment pins in place of the pin-positioning holes 1102, and thealignment pins' would function to connect to pin-positioning holes in aferrule.

The apparatus for holding an optical element 1100 has multipleadvantages and uses. First, it permits holding and manipulating thefirst ferrule 112 in both the x, y, and z direction as well asrotational directions. This aids in achieving precise alignment andattachment of the first ferrule 112 to the optoelectronic devices 106.Also, the apparatus for holding an optical element 1100 grasps the firstferrule 112 without interfering, obscuring or damaging the opticalfibers 114 in the first ferrule 112. Additionally, the apparatus forholding an optical element 1100 allows access to the optical fibers 114in the first ferrule 112 so that optical coupling may be achieved. Forexample, a light may be mounted on top of the apparatus for holding anoptical element 1100 so that the optical fibers 114 emit light whilebeing held by the apparatus for holding an optical element 1100. Thelight emitted from the fibers 114 may then be used to aid in opticallycoupling the first ferrule 112 to the optoelectronic devices 106.Conversely, light from the optoelectronic devices may be used to aid inoptically coupling the first ferrule 112 to the optoelectronic devices106. Additionally, the apparatus for holding an optical element 1100provides a strain-less release mechanism through the use of the vacuumclamp. By simply turning off the vacuum pressure, the apparatus forholding an optical element 1100 gently releases the first ferrule 112.

The apparatus for holding an optical element 1100 also may be used for avariety of different purposes other than holding a ferrule. For example,it may be used to align and attach a micro-pipette array to a biologicalsensor array or a lens array to a MEMS modulator array. It also may beused to attach a single or array of optical fibers to a variety ofdifferent objects or devices. Moreover, the optical element may be a MTtype connector, ferrule, MT like ferrule, lenslet array, a diffractiveoptical element or any other type of device that may be aligned with thedevice. Accordingly, the apparatus for holding an optical element 1100has multiple advantages and uses.

C. Alignment Process—X, Y and Rotational Directions

Once the first ferrule 112 is held at the end of the high precision armby the apparatus for holding an optical element 1100, the next step isto align the optical fibers with the optoelectronic devices in the x, yand rotational directions. In this section, three different alignmentprocess are described.

1. Image Alignment Process

The first process for aligning the optical fibers with theoptoelectronic devices in the x, y and rotational directions is an imagealignment process. In this embodiment of the invention, a split-fieldmicroscope is used to align the optical fibers with the optoelectronicdevices by super-imposing an image of at least one optical fiber with animage of at least one optoelectronic devices. Specifically, once thefirst ferrule 112 is held at the end of the high precision arm by theapparatus for holding an optical element 1100, the array ofoptoelectronic devices, which are mounted on a flexible printed circuitboard, are held on a high-precision stage. A top-down view camera may bemounted above the high-precision stage holding the optoelectronicdevices. With the aid of a split-view microscope and a split-field opticvideo system, a top-down image of the flexible printed circuit board102, situated on the high precision stage, is displayed on a monitor.

The focus and zoom on the split-field microscope and or the stageholding the flexible printed circuit board are adjusted until theoptoelectronic devices 106 that are adapted to the flexible printedcircuit board 102 are in view on the video monitor. The top surface ofthe array of optoelectronic devices 106 appears as rings 1202 on thevideo monitor under the high magnification of the microscope, as shownin FIG. 12 a. A split-field video system permits simultaneous viewing oftwo opposite corners 1204 or ends of the array of optoelectronic devices106 with high magnification on the video monitor. The precision stageholding the flexible printed circuit board is adjusted until the firstoptoelectronic device 1206 and the twelfth optoelectronic device 1208are displayed simultaneously on the video monitor, as shown in FIG. 12b.

A light is mounted above the high-precision arm, emitting opticalradiation down into the optical fibers 114 that are packaged in thefirst ferrule 112. The light flowing down the optical fibers back-lightsthe fiber cores, and this provides a well-resolved image of the fibercores under the split-field microscope. The image of the cores thenappear as an array of well-resolved spots under the split fieldmicroscope, as shown in FIG. 12 c.

Once the split-field microscope has formed an image of the fiber coresand an image of the optoelectronic devices, these two images are thensuperimposed by the split-field microscope to perform the alignmentprocess. Specifically, by adjusting the x and y position of thehigh-precision stage, the image of the illuminated fiber cores of thefirst optical fiber 1212 and twelfth optical fiber 1214 are alignedwithin the image of the rings of the first optoelectronic device 1206and twelfth optoelectronic device 1208 via the split-field microscope sothat the spots and rings form a bull's eye pattern, as shown in FIG. 12d. This process precisely aligns in the x, y and rotational directionthe array of optical fibers 114 that are packaged in the first ferrule112 with the array of optoelectronic devices 106 that are adapted to theflexible printed circuit board 102. In another embodiment, images of theoptical fibers and optoelectronic devices other than the images of thefirst and twelfth optical fibers and optoelectronic devices may be usedto achieve the same result.

2. Optical Energy Alignment Process

A second process to align the optical fibers with the optoelectronicdevices in the x, y and rotational directions is an optical energyalignment process. In this embodiment of the invention, the flexibleprinted circuit board is again held by a high-precision stage. A lightis mounted above the high-precision arm that holds the first ferrule,and the light emits optical radiation down into the optical fibers 114that are packaged in the first ferrule 112. The light flowing out of theoptical fibers 114 radiates down onto the flexible printed circuit board102, which is positioned on the high-precision alignment stage. Underthe high magnification of a microscope, this light appears as a seriesof illuminating spots on the optoelectronic devices 106. Eachilluminating spot corresponds to an optical fiber in the array ofoptical fibers 114 that are packaged in the first ferrule 112. Byadjusting the x and y position of the high-precision stage, the spotsmay be visually aligned with the rings to form a bull's eye patternunder the high magnification of a microscope. (This alignment processmay be performed by machine vision rather than by human vision.) Thealignment process precisely aligns in the x, y and rotational directionthe array of optical fibers 114 that are packaged in the first ferrule112 with the array of optoelectronic devices 106 that are adapted to theflexible printed circuit board 102.

3. Precision Placement Alignment System

A third process to align the optical fibers with the optoelectronicdevices in the X, Y and rotational directions is a precision placementsystem. In this embodiment of the invention, a precision placementsystem is connected to a high-precision arm that holds the firstferrule, and the system also is connected to a high-precision stage thatholds the optoelectronic devices. The precision placement system alignsthe objects by first calculating their initial position in space bycomparing their position to a known position in space. Based upon thisinformation, the system calculates the relative distances that theobjects are apart. Once the relative distances are determined, theprecision placement system aligns the objects by sequentially moving theobjects and re-calculating their relative distances until they areprecisely aligned.

In one embodiment of the invention, the precision placement system maydetermine the initial position in space of the array of optical fibersand the optoelectronic devices by holding the objects within a field ofview of a microscope. Since the position of the cross-hairs on themicroscope is known, the precision placement system knows the positionof the optical fibers and optoelectronic devices relative to theposition of the cross-hairs. Based upon this information, the precisionplacement system then calculates the relative positions of the objectsto each other. Knowing the relative distances, the precision placementsequentially and continually moves the position of the objects andre-calculates their relative positions to each other until the opticalfibers and optoelectronic devices are precisely aligned.

In another embodiment of the invention, the precision placement systemmay determine the initial position in space of the array of opticalfibers and the optoelectronic devices by moving the objects to a pointin space whose position is already known by the system. For example, thesystem may move the objects to corner mark on a jig or a precision touchsensor. Once the objects are referenced to that point in space, theprecision placement system can calculate their relative positions toeach other. The precision placement system then sequentially moves theposition of the objects while continually re-calculating their relativepositions to each other until they are precisely aligned.

D. Alignment Process—Z Axis Direction

Once the optical fibers 114 and optoelectronic devices 106 are alignedthe X, Y and rotational directions, the high-precision alignment arm islowered until the first ferrule 112 is within a few microns from theoptoelectronic devices 106. This vertical or Z-axis alignment process isaccomplished through the use of a video-image measuring system thatfunctions in concert with the previously-described precision equipment.This z-axis alignment process is described below.

A video-image measuring system is connected between a monitor and aside-view camera that is mounted near the side of the high-precisionstage. With the aid of the microscope, the side-view camera views theside of the optoelectronic devices 106 and first ferrule 112, and thisimage is displayed on the monitor.

FIG. 13 is a view of the monitor when using the video-image measuringsystem. The video image measurement system generates positionalmeasuring lines 1302 over the images on the monitor, and the lines 1302allow a user to measure the vertical distance or Z-axis height between abottom edge 1304 of the first ferrule 112 and a top edge 1306 of theoptoelectronic devices 106, as shown in FIG. 13. By adjusting the zposition of the high-precision arm and the high-precision stage, thedistance between the bottom edge 1304 of the first ferrule 112 to thetop edge 1306 of the optoelectronic devices 106 is adjusted until theobjects are within a few microns (e.g., approximately 35 microns apart).Accordingly, a gap exists between the first ferrule 112 and theoptoelectronic devices 106.

In another embodiment of the process, the z-axis alignment process maybe accomplished by using laser-triangulation, interference microscophyor a touch sensor.

E. Mechanical Stabilization Process

After the first ferrule 112 and optoelectronic devices 106 are preciselypositioned in space, the high-precision placement arm is raised, movingthe first ferrule 112 away from the optoelectronic devices 106 in thevertical or Z-axis direction. A small volume of first adhesive 116 isthen dispensed on the top surface of the optoelectronic devices 106 by ahigh precision, motor-driven syringe.

The high-precision placement arm is again lowered in the vertical orZ-axis direction until the first ferrule 112 contacts the opticaladhesive 116, which has been dispensed on the top surface of theoptoelectronic devices 106. The first ferrule 112 is suspended above thetop surface of the optoelectronic devices in the liquid optical adhesive116. The first adhesive 116 may be cured using a UV light curing system.

At this point, the first ferrule 112 is attached to the optoelectronicdevices 106 with the first adhesive 116 and is held from above by theapparatus for holding an optical element 1100. As previously stated, thefirst adhesive mechanically stabilizes the first ferrule 112 to theoptoelectronic devices 106. The first ferrule 112 is separated from theapparatus for holding an optical element 1100 releasing the vacuum clampon the apparatus for holding an optical element 1100 and raising thehigh precision alignment arm.

To further mechanically stabilize the first ferrule 112 to the headregion 302 of the flexible printed circuit board 102, a dam 120 may beformed on the flexible printed circuit board 102 and filled with thesecond adhesive 122. A software-controlled dam and dam fill dispensingmachine may be used to apply the dam 120 on the first surface 310 of thehead region 302 of the flexible printed circuit board 102.Alternatively, the dam and filling process may be done manually. The dam120 is formed on the first surface 310 of the head region 302 of theflexible printed circuit board 102 surrounding the first ferrule 112,driver or amplifier chip 108 and any other electrical components. Thedam 120 is composed of an adhesive.

Once the dam 120 is formed on the flexible printed circuit board 102,the automated fluid dispensing machine may be used to fill the areawithin the dam 120 with the second adhesive 122, as shown in FIG. 3 a.The second adhesive 122 may be cured by placing the flexible printedcircuit board 102 in an oven. After curing, the first ferrule 112becomes further mechanically stabilized to the first surface of the headregion 302 of the flexible printed circuit board 102.

F. Automating the Alignment Process

The entire process of precisely aligning and attaching the first ferrule112 to the optoelectronic devices 106 and mechanically stabilizing it tothe flexible printed circuit board 102 may be done manually.Alternatively, this process may be done automatically through the use ofa computer generated system that functions in concert with theabove-described precision equipment. Accordingly, this process iscompatible with a mass-production manufacturing process that is the typeof technology that is necessary to lower the cost of anycommercially-available high-volume product.

G. Other Applications

Although an embodiment of the invention has been discussed in terms ofaccurately aligning and attaching an array of optical fibers to an arrayof optoelectronic devices, the same methodology may be employed toaccurately align and connect an array of optical fibers to a widevariety of devices or objects other than optoelectronic devices. This isbecause there is a trend to miniaturization in many fields of scienceand technology that require work pieces to be positioned to a fewmicrons and many times to sub-microns. Such fields include optics,microscopy, semiconductor technology, micro-machining, the life sciencesand others. Accordingly, an embodiment of the invention may be used, forexample, to accurately align and connect optical fibers to a microscopeslide so as to study fluorescence light emitted from a biological samplesuch as a gene or insect. The light may be collected by the opticalfibers and transmitted to a spectrometer for study. In another example,an embodiment of the invention may be used to accurately align andconnect an array of optical fibers to micro-electromechanical systems(“MEMS”). MEMS technology involves combining semiconductor andmicro-machining processes to produce tiny devices that are capable ofmotion on a microscopic scale on a silicon substrate. These systems mayutilize the technology contained in an embodiment of the invention toaccurately align and connect an array of optical fibers to the tinydevices in the micro-electromechanical system for a wide variety ofapplications. Consequently, an embodiment of the invention may be usedto couple an array of optical fibers to a wide variety of devices orobjects.

Finally, although an embodiment of the invention has been discussed interms of passive alignment, an embodiment of the invention allows foractive alignment and attachment of the array of optical fibers to anarray of optoelectronic devices. As explained earlier, this processinvolves manually manipulating and connecting the optical fibers to theoptoelectronic devices. While we have described our preferredembodiments of the present invention, it is understood that thoseskilled in the art, both now and in the future, may make variousimprovements and enhancements that fall within the scope of the claimsthat follow. These claims should be construed to maintain the properprotection for the invention first disclosed.

1. A flexible printed circuit board comprising: a) a main body regionorientated in a first direction having at least one electrical device;b) a plurality of electrical contact pads integrated into the main bodyregion, where the electrical contact pads are capable of connecting theflexible printed circuit board to an external environment; c) a buckleregion extending from one end of the main body region; d) a head regionextending from one end of the buckle region, and where the head regionis orientated so that it is at an angle relative to the direction of themain body region; and e) a spacer that is adapted to the head region ofthe flexible printed circuit board, wherein the spacer is capable ofacting as a mounting surface for at least one optoelectronic device. 2.An apparatus as in claim 1, wherein the external environment is a secondcircuit board.
 3. An apparatus as in claim 1, wherein at least oneoptoelectronic device comprises a photo-detector.
 4. An apparatus as inclaim 1, wherein at least one optoelectronic device comprises a verticalcavity surface emitting laser.
 5. An apparatus as in claim 4, whereinthe vertical cavity surface emitting laser comprises an oxide verticalcavity surface emitting laser.
 6. An apparatus as in claim 1, furthercomprising at least one optoelectronic device adapted to the headregion.
 7. An apparatus as in claim 6, wherein at least oneoptoelectronic device comprises a photo-detector.
 8. An apparatus as inclaim 6, wherein at least one optoelectronic device comprises a verticalcavity surface emitting laser.
 9. An apparatus as in claim 8, whereinthe vertical cavity surface emitting laser comprises an oxide verticalcavity surface emitting laser.
 10. An apparatus as in claim 1, whereinthe electrical contact pads are adapted to a first surface or a secondsurface of the main body region.
 11. An apparatus as in claim 1, whereinthe electrical contact pads are ball grid arrays.
 12. An apparatus as inclaim 1, wherein the electrical contact pads are solder balls.
 13. Anapparatus as in claim 1, wherein the electrical contact pads areland-grid arrays.
 14. An apparatus as in claim 1, further comprising anoptical power control system adapted to the head region of the flexibleprinted circuit board.
 15. An apparatus as in claim 1, furthercomprising a driver or amplifier chip adapted to the head region or mainbody region of the flexible printed circuit board.
 16. An apparatus asin claim 1, further comprising a plurality of conducting lines that areadapted to the head region, the buckle region and the main body region.17. A flexible printed circuit board comprising: a) a main body regionorientated in a first direction having at least one electricalcomponent; b) a buckle region extending from one end of the main bodyregion; c) a head region extending from one end of the buckle region,and where the head region is orientated so that it is at an anglerelative to the direction of the main body region; and d) a heightadjuster adapted along at least a portion of a surface of the headregion of the flexible printed circuit board.
 18. An apparatus as inclaim 17, further comprising at least one optoelectronic device adaptedto the head region.
 19. An apparatus as in claim 18, wherein at leastone optoelectronic device comprises a photo-detector.
 20. An apparatusas in claim 18, wherein at least one optoelectronic device comprises avertical cavity surface emitting laser.
 21. An apparatus as in claim 20,wherein the vertical cavity surface emitting laser comprises an oxidevertical cavity surface emitting laser.
 22. An apparatus as in claim 17,wherein the head region is orientated in such a manner so that it issubstantially perpendicular to the direction of the main body region.23. An apparatus as in claim 17, wherein the height adjuster is capableof changing the height of at least one electrical or optoelectroniccomponent on the head region.
 24. An apparatus as in claim 17, furthercomprising wire leads adapted to the main body region.
 25. An apparatusas in claim 17, further comprising electrical contact pads integratedinto the main body region, wherein the electrical contact pads arecapable of connecting the flexible printed circuit board to an externalenvironment.
 26. An apparatus as in claim 25, wherein the externalenvironment comprises a circuit board.
 27. An apparatus as in claim 25,wherein the electrical contact pads are adapted to a first surface or asecond surface of the main body region.
 28. An apparatus as in claim 25,wherein the electrical contact pads are ball grid arrays.
 29. Anapparatus as in claim 25, wherein the electrical contact pads are solderballs.
 30. An apparatus as in claim 25, wherein the electrical contactpads are land-grid arrays.
 31. A flexible printed circuit boardcomprising: a) a main body region orientated in a first direction havingat least one electrical component; b) a buckle region extending from oneend of the main body region; c) a head region extending from one end ofthe buckle region, and where the head region is orientated so that it isat an angle relative to the direction of the main body region; d) a heatspreader adapted along at least a portion of a surface of the headregion of the flexible printed circuit board; e) a window in the headregion of the flexible printed circuit board, the window capable ofproviding access to the heat spreader; and f) an optical power controlsystem adapted to the head region of the flexible printed circuit board.32. An apparatus as in claim 31, further comprising at least oneoptoelectronic device adapted to the heat spreader in such a manner thatat least one optoelectronic device is accessible through the window inthe flexible printed circuit board.
 33. An apparatus as in claim 32,wherein at least one optoelectronic device comprises a photo-detector.34. An apparatus as in claim 32, wherein at least one optoelectronicdevice comprises a vertical cavity surface emitting laser.
 35. Anapparatus as in claim 34, wherein the vertical cavity surface emittinglaser comprises an oxide vertical cavity surface emitting laser.
 36. Anapparatus as in claim 31, wherein the heat spreader provides mechanicalrigidity or stiffness to the head region of the flexible printed circuitboard.
 37. An apparatus as in claim 31, wherein the head region isorientated in such a manner so that it is substantially perpendicular tothe direction of the main body region.
 38. An apparatus as in claim 31,further comprising a driver or amplifier chip adapted to the head regionor main body region of the flexible printed circuit board.
 39. Anapparatus as in claim 31, further comprising a plurality of conductinglines that are adapted to the head region, the buckle region and themain body region.
 40. An apparatus as in claim 31, further comprisingwire leads adapted to the main body region.
 41. An apparatus as in claim31, further comprising electrical contact pads integrated into the mainbody region, wherein the electrical contact pads capable of connectingthe flexible printed circuit board to an external environment.
 42. Anapparatus as in claim 41, wherein the external environment comprises acircuit board.
 43. An apparatus as in claim 41, wherein the electricalcontact pads are adapted to a first surface or a second surface of themain body region.
 44. An apparatus as in claim 41, wherein theelectrical contact pads are ball grid arrays.
 45. An apparatus as inclaim 41, wherein the electrical contact pads are solder balls.
 46. Anapparatus as in claim 41, wherein the electrical contact pads areland-grid arrays.
 47. A flexible printed circuit board comprising: a) amain body region orientated in a first direction having at least oneelectrical component; b) a buckle region extending from one end of themain body region; c) a head region extending from one end of the buckleregion, and where the head region is orientated so that it is at anangle relative to the direction of the main body region; d) a heightadjuster adapted along at least a portion of a surface of the headregion of the flexible printed circuit board; and e) a window in thehead region of the flexible printed circuit board, the window capable ofproviding access to the height adjuster.
 48. An apparatus as in claim47, further comprising at least one optoelectronic device adapted to theheight adjuster in such a manner that at least one optoelectronic deviceis accessible through the window in the flexible printed circuit board.49. An apparatus as in claim 48, wherein at least one optoelectronicdevice comprises a photo-detector.
 50. An apparatus as in claim 48,wherein at least one optoelectronic device comprises a vertical cavitysurface emitting laser.
 51. An apparatus as in claim 50, wherein thevertical cavity surface emitting laser comprises an oxide verticalcavity surface emitting laser.
 52. An apparatus as in claim 47, whereinthe height adjuster provides mechanical rigidity or stiffness to thehead region of the flexible printed circuit board.
 53. An apparatus asin claim 47, wherein the head region is orientated in such a manner sothat it is substantially perpendicular to the direction of the main bodyregion.
 54. An apparatus as in claim 47, further comprising an opticalpower control system adapted to the head region of the flexible printedcircuit board.
 55. An apparatus as in claim 47, further comprising adriver or amplifier chip adapted to the head region or main body regionof the flexible printed circuit board.
 56. An apparatus as in claim 47,further comprising a plurality of conducting lines that are adapted tothe head region, the buckle region and the main body region.
 57. Anapparatus as in claim 47, further comprising wire leads adapted to themain body region.
 58. An apparatus as in claim 47, further comprisingelectrical contact pads integrated into the main body region, whereinthe electrical contact pads capable of connecting the flexible printedcircuit board to an external environment.
 59. An apparatus as in claim58, wherein the external environment comprises a second circuit board.60. An apparatus as in claim 58, wherein the electrical contact pads areadapted to a first surface or a second surface of the main body region.61. An apparatus as in claim 58, wherein the electrical contact pads areball grid arrays.
 62. An apparatus as in claim 58, wherein theelectrical contact pads are solder balls.
 63. An apparatus as in claim58, wherein the electrical contact pads are land-grid arrays.
 64. Aflexible printed circuit board comprising: a) a substantiallyrectangular main body region with two short sides and two long sides,the main body region having at least one electrical device adaptedthereto; b) a buckle region extending from one of the short sides of themain body region; c) a head region extending from the buckle region in aplanar orientation substantially perpendicular to the main body region;d) a head region having at least one optoelectronic device thereon, theoptoelectronic device situated substantially along a longitudinal axisof the flexible printed circuit board; and e) a spacer that is adaptedto the head region of the flexible printed circuit board, wherein thespacer is capable of functioning as a mounting surface for theoptoelectronic devices.
 65. An apparatus as in claim 64, wherein atleast one optoelectronic device comprises a photo-detector.
 66. Anapparatus as in claim 64, wherein at least one optoelectronic devicecomprises a vertical cavity surface emitting laser.
 67. An apparatus asin claim 66, wherein the vertical cavity surface emitting lasercomprises an oxide vertical cavity surface emitting laser.
 68. Anapparatus as in claim 64, further comprising an optical power controlsystem adapted to the flexible printed circuit board.
 69. An apparatusas in claim 65, further comprising a driver or amplifier chip adapted tothe head region or the main body region of the flexible printed circuitboard.
 70. An apparatus as in claim 64, further comprising a pluralityof conducting lines that are adapted to the head region, the buckleregion and the main body region.
 71. An apparatus as in claim 64,further comprising wire leads adapted to the main body region.